2 Types of Trailer plates were
issued. TP for Pneumatic tires,(air-filled),
and TS for Solid tires. T.P.2 means Trailer- Pneumatic-(up to) 2
axle.
All plates shown except the 1932-33 are made of steel.

* The 1928 repaint shown above is still a mystery but I
will unofficially call it a trailer plate for now.
These motorcycle-sized T prefix oddities are county-coded with a
Maricopa County plate
known with number T-1/698. A very high number for it to be none
other than a trailer plate
of which there were over 600 trailers registered in Maricopa
County for 1928.( 1928 is from a private collection )